Pile-driving system and apparatus

ABSTRACT

A system for driving piles by a succession of blows struck from above by a hammer element wherein a driving head assembly transfers the blow to the upper end of a hollow elongated pile. The driving head comprises an anvil element to engage the upper end of a pile and includes an elongated hollow case extension portion containing the reciprocable hammer element. A cable connected to the hammer element extends upwardly to an outdoor work platform for hoisting and lowering the driving head assembly. A pulley driven by hydraulic actuator means provides reciprocating movement to the hammer element.

United States Patent 12/1933 McNeilly 72 Inventor Samuel CliffordDoughty 1,938,459 173/86 Burlingame, Calif. 2,342,253 2/1944 Copley173/88 [2]] Appl, No. 756,685 2,721,055 10/1955 Madson et a]. 175/293[22] Filed Aug. 30, 1968 FOREIGN PATENTS 145] sew-14,1971 536,133 4/1922France 61/535 {73] Asslgnce Santa Fe International Corporation Santa Fesprings, m Primary Examiner.lames A. Leppink AttorneyFlehr, Hohbach,Test, Albritton & Herbert [54] FILE-DRIVING SYSTEM AND APPARATUS C aimssnrawmg Figs ABSTRACT: A system for dr1v1ng p1les by a successlon ofU.S. blo tru k from above a hammer element wherein a driv- 175/17l inghead assembly transfers the blow to the upper end ofa holl w elongat dThe driving head comprises an anvil ele- 501 Field of Search 173/81-89,mm to engage the upper end f a pile and includes an elm 80, 128133, 134,136, 137, 139; 175/6, 17 gated hollow case extension portion containingthe reciproca- 56 ble hammer element. A cable connected to the hammerele- 1 References cued ment extends upwardly to an outdoor work platformfor hoist- UNITED STATES PATENTS ing and lowering the driving headassembly. A pulley driven by 863,614 8/1907 Lake 175/6 hydraulicactuator means provides reciprocating movement to 948,989 2/1910 Coffey173/86 the hammer element.

0 I I I M :4. 41 11 .1 a

n F a 11 PATENTED SEPI 4 |97l SHEET 1 OF 3 mvrsmon Samuel CliffordDoughty BY Attorneys PATENTED SEPI 419m "sum 2 or 3 IN'VENTOR.

Samuel Clifford Dou BY PATENTEU .SEP 1 4|91| SHEET 3 OF 3 12 F i g. 8

i l A A [ii 2 F i 7 INVEIJfOR Samuel Clifford Doughty w W M fW AttorneysPILE-DRIVING SYSTEM AND APPARATUS BACKGROUND OF THE INVENTION Thisinvention pertains to a system for driving piles by a succession ofblows struck from above by a hammer element and to apparatus for use insuch system. This invention is particularly useful in driving piles intothe ocean floor under great depths of water, though not limitedexclusively to such application.

In the construction of offshore drilling platforms and other downwardlyextending legs form the so-called jacket" or support tower structure forthe offshore platform.

It is necessary to resist overturning forces of wind and sea as well asother overturning forces. This, in the past, has been done by means ofproviding elongated piles which penetrate to .great depths and to whichthe tower can be secured by means of locating the piles coaxially of thehollow legs of the tower.

In order to drive piles coaxially of such jacket legs at greater andgreater depths, it is becoming increasingly necessary to apply greaterand greater hammering energy to the pile, preferably from theconvenience of outdoor work stations rather than from submarinelocations. It has been ob- .served that losses in the transmission ofenergy can occur where a pile extension is disposed atop the upper endof the pile to permit the blow to be struck at such an outdoor workstation above the surface of the ocean. Certain follower mechanisms havealso been employed but are'also believed to suffer from the samedisadvantage. However, in order to employ larger and larger hammerelements or rams for striking the pile and for other reasons, andnotwithstanding the inherent energy losses, it has remained preferableto drive the pile from the outdoor work station rather than to insertcompressed air and steam hammers down into the leg of the towerstructure for operation below the surface of the water.

Thus, while it is desirable to transmit the hammer energy substantiallydirectly to the pile without loss of energy and by extremely massivehammer elements which can be readily operated from the outdoor workstation at the top of the tower ,or on the platform supported by thetower, these objectives have been somewhat incompatible.

Where underwater steam and air hammers have been attempted for use atsubmerged locations within the tower legs, trouble has'been experiencedin discharging the exhaust of such devices into the air above the watersince this is usually done by carrying a heavy hose downwardly throughthe water and coupling it to the hammer. This hose must be very strongto overcome the tendency to collapse under high external water pressure.Other difficulties to be overcome are condensation of both live andexhaust steam when carried to great depths throughcold water, wherebythe hammer mechanism tends to become drowned in a pocket of watercondensate which impairs its functioning.

Other difficulties in the past have stemmed from the presence ofinfiltrated water under-high pressure finding its way into the casing soas to come between the contacting surface of the falling ram or hammerand top of the driving block or anvil which transmits the blow to thepile. Any such intrusion of water, in view ofits incompressible nature,greatly dissipates the energy of the blow of the hammer and renders itsignificantly lesseffective. Such water intrusion difficulties in thepast have been countered by introducing compressed air into the casingso as ,to provide sufficiently high pressure to drive out thewater.However, difficulties have impaired the driving efficiency of underwaterhammers of this type. Furthermore, such underwater hammers have seldombeen as used to apply a striking blow to the upper end of a pile to beused at great depths of water, for example, at depths appreciablyexceeding more than a hundred feet.

OBJECTS It is, in general, an object of the present invention to providean improved pile-driving system and improved apparatus therefor whichovercomes the foregoing and other problems.

It is another object to provide a drop-hammer style of piledrivingsystem for submarine driving of piles. I

It is another object of the present invention to provide a pile-drivingsystem and apparatus which inherently'minimizes the loss of energytransmitted by the ram or hammer element driven.

It is yet another object of the invention to provide an improved piledriving apparatus wherein reactive forces derived from a column of watercaptured within the pile being driven are dissipated without substantialloss of energy from the piledriving blow.

SUMMARY OF THE INVENTION In general, there is provided a system fordriving piles by a succession of blows struck from above by a hammerelement. A driving head assembly is adapted to transfer the blows to theupper end of the pile and comprises an anvil element adapted to engagethe upper end of the pile in blow-transmitting relation thereto. Anelongated hollow case is secured at one end of the anvil element so asto form an extension thereof. A massive hammer element is movablebetween advanced and retracted positions within the case to strike thenecessary blows against the anvil. A flexible cable, connected to oneend of the hammer element, lifts and lowers both the hammer ele-' mentand driving head assembly and also serves to operate the drop hammeraction by an actuator means supporting thecable. Actuator means locatedat an outdoor work station serves to lift and quickly release the cablerepetitively to provide' a succession of rapid blows struck by thefalling hammer element.

These and other objects of the invention will be'more clearly understoodfrom the following detailed description of preferred embodiments whenconsidered in conjunction with the accompanying drawings and generalsummary of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevation schematic viewshowing an offshore oil drilling platform of the type referred to above;

FIG. 2 is an enlarged elevation view (partly in further enlargedsection) schematically showing a pile-driving system and apparatusaccording to the invention;

FIG. 3 is a section view taken along the line 3-3 of FIG. 2;

FIG. 4 diagrammatically shows a system for operating the actuator meansfor providing a drop hammer action;

FIG. 5 is an enlarged detail view, in section, of another embodiment ofa driving head assembly according to the invention;

FIG. 6 is an enlarged detail view showing an improved-pile constructionaccording to the invention;

FIG. 7 is an elevation view showing another embodiment of the systemaccording to the invention;

FIG. 8 is an enlarged elevation section view of a detail portion of FIG.7 taken in the region of the line 88;

DESCRIPTION OF THE PREFERRED EMBODIMENTS As noted above, thepile-driving system as disclosed herein may be advantageously employedin offshore pile-driving rigs of a type, for example, as shown inFIG. 1. Thus, the superstructure 11 of the rig is generally located onor above the surface of the water 12 by means of a rather tall supporttower 13. In general, the support tower 13 has been referred to as ajacket" comprised of upstanding'legs 14 which are suitably braced andsupported and generally angle downwardly and outwardly from thesuperstructure 11 at an angle to the vertical.

As they participate in the system disclosed herein, legs 14 aregenerally hollow tubular members forming pile guide channels. Tower 13typically is secured to the ocean floor 16 by means of hollow pilescoaxially inserted snugly into the hollow interior of legs 14 so thatthey may be driven downwardly into the ocean floor to great depths inorder to penetrate well beyond the relatively soft upper material of theocean floor. Piles 17 form a close sliding fit within legs 14.

The upper ends of piles 17 are typically left in place to extendupwardly above the ocean floor 16 an amount sufficient to provide thenecessary stability to the rig.

A guide channel, other than legs 13 can, of course, be defined in otherways. For example, in the application of offshore drillingcircumstances, for example, so-called skirt piles are driven through andguided by short tubular lengths secured to the exterior portions of thejacket. Further, annular guide rings are sometimes employed incircumstances of the above type wherein several piles are used within asingle leg of the structure.

In view of the fact that the legs 14 and the piles 17 are of relativelylarge diameter, on the order of several feet in diameter, and in view ofthe exceptional length of such piles, for example on the order ofseveral hundred feet, it is highly desirable to minimize the amount ofpile extension lodged within the legs 14 consistent with safety to thetower.

Thus, where piles 17 extend the full length of legs 14, it will bereadily evident that a considerable waste of expensive piles 17 hasoccurred in view of the fact that the uppermost portions of such pilesare providing little or no supporting or stabilizing function.

In order to conquer this problem in the past, it has been suggested toemploy the pile-driving follower or extension, as mentioned earlier,which can be struck at its upper end in the region of the outdoor workstation on platfonn 18 where the energy will be transmitted indirectlythrough the pile extension or follower to the upper end of the pilelocated well down in the leg. As noted, these systems have been subjectto severe energy losses in providing such indirect force-transmittingmeans.

Referring to FIG. 2, a pile driving system is shown wherein the upperend of a pile 17 is shown disposed in a hollow leg 14 of support tower13. A driving head assembly 19 comprised generally of those componentsshown in the enlarged detail portion of FIG. 2 is seated in the openupper end of pile 17.

Thus, the driving head assembly comprises an anvil element 21 adapted toengage the upper end of the pile 17 in blowtransmitting relation. Anvilelement 21 includes a tapered frustoconical portion 211 dimensioned andadapted to fit readily into the upper end of pile 17 and to be supportedby an enlarged annular midsection 21b serving to form a shoulder 22which rests upon the upper edge of pile 17. The other end of anvilelement 21 is formed to include a portion 210 of slightly reduceddiameter and formed with a top face 23, which preferably can be slightlydomed, to constitute the striking face of the anvil element 21 whichdirectly receives the blows of a longitudinally movable ram or hammerelement 24.

Portion 21c serves to plug and seal the lower open end of an elongatedhollow case 26 secured to the upper end of anvil element 21 in a mannerto form an extension of anvil 21 whereby both anvil 21 and case 26travel together in a following movement as the pile 17 penetrates intothe earth. Anvil 21 and its case extension 26 fit closely within the leg14 in sliding manner comparable to the sliding fit between pile l7 andleg 14.

Anvil element 21 may, forexample, be of solid steel material or may beformed in a manner described further below relative to an additionalembodiment pertaining to same.

While anvil element 21 serves to seal the lower end of case 26, theupper end of case 26 is also substantially sealed whereby the interiorof case 26 is subjected to air pressure from an airhose 27 connected topressurize case 26 through a compressed air inlet 28. At the lower endof case 26, an outlet 29 of a type serving to pass water while retainingair pressure within case 26, and of known construction, serves toevacuate any accumulated liquid from within case 26 under the airpressure from inlet 28.

Hammer element 24, as noted, moves through a stroke 31 to supply asuccession of blows against the striking face 23 of anvil element 21. Inorder to eliminate any dissipation of the striking energy derived fromthe falling hammer element 24by virtue of any accumulated cushion of airdisposed between the lower end of hammer element 24 and the strikingface 23, as might otherwise form at that location by virtue of theclosely fitted guided relation existing between the periphery of hammerelement 24 within the closed case 26, fluid passage means have beenformed longitudinally of the case and hammer for transferring fluid(such as air) therealong during movement of the hammer within the case.

Thus, as shown best in FIG. 3, fluted portions 32 form longitudinallyextending peripheral indentations in the cross section of hammer element24 in the nature of grooves to provide sufficient clearance to transferany entrapped air at the lower end of the falling hammer element 24 tothe increasing space at the upper end of hammer element 24. In order tomaintain a closely fitting guiding relation between hammer element 24and case 26 to minimize any side movement and undesirable lateralvibration forces, longitudinally extending ribs 33 are provided. Ribs 33formed between each adjacent pair of fluted portions 32 ride along theinterior wall of case 26.

With the foregoing configuration, it becomes readily possible to employan extraordinarily massive hammer element 24 on the order, for example,of many thousands of pounds. A hammer element of such scope, if notclosely contained within its guiding case can, of course, cause seriouslateral impact forces acting against and damaging to the structure ofthe support tower 13.

Means for reciprocating hammer element 24 serves to lift it through itspredetermined stroke 31 and then release the hammer element to fallfreely to an advanced position where it contacts the striking face 23.Flexible cable means have been provided connected to the upper end ofhammer element 24 in the form of a flexible steel cable 34 anchored inthe upper end of hammer element 24 by suitable known means for embeddinga cable in a solid steel material. A watertight packing gland 36 locatedin the upper end of case 26 passes cable 34 outwardly thereof so thatcable 34 is free to move in and out of case 26 to lift and releasehammer 24.

Means for actuating the cable so as to move hammer ele ment 24 betweenlowered and raised positions as well as to continuously pay outadditional cable to operate the hammer at increasing depths as the pilepenetrates the earth includes the structure shown at the upper end ofsupport tower 13.

Thus, at the outdoor work station 18, a work surface or mountingplatform 37 supports hoisting means which serves to pay out and retrieveboth case 26 and hammer element 24 as well as to anchor or hold theupper end of cable 34. Thus, the hoisting means is in the form of anengine 38 of a suitable type readily controllable by an operator orattendant 39. Engine 38 is suitably coupled, as by means of the driveconnection 41, to rotate the Windlass portion 42 of a winch 43. Thus,winch 43 serves to wrap and unwrap cable 34 upon Windlass 42.

A pulley 44 formed with a relatively deep sheave groove 46 engages thatportion of cable 34 defined between Windlass 42 and the upper end of leg14. As Windlass 42 is operated in a direction to pay out the cable 34,the airhose 27 may also be paid out accordingly so as to extenddownwardly along leg 14. Airhose 27 is, therefore, conveniently carriedupon a retractable hose reel 47 mounted to platform 37 so as to permitthe airhose to be readily paid out along the other end of reel 47.

The upper end of airhose 27 is coupled to an air compressor 48 carriedby platform 37. 7

Means for actuating pulley 44 to move between advanced and retractedpositions so as to quickly relieve the tension in cable 34 and permithammer element 24 to fall freely under the force of gravity includes thehydraulically. operated actuator 49 (FIG. 4). Actuator 49 is adouble-acting hydraulic piston operated by suitable fluid system meanswhereby lines 51, 52 are alternately and quickly respectively connectedto pressure and exhaust lines of a hydraulic pump 53.

The system shown in FIG. 4 for alternately applying pressure and exhaustto the opposite ends of hydraulic actuator 49 is merely representativeof a number of systems for providing the function of developing a greatforce quickly acting to raise and to lower the pulley 44 through itspredetermined stroke. From the foregoing, it will be evident that, inthe condition shown, the spool style control element 58 serves to couplefluid line 52 to pressure from pump 53 via line 54 while connectingfluid line 51 to exhaust fluid to the pump via line 57. It is to befurther understood, of course, that suitable reservoirs and otherconventional hydraulic system devices may be employed to round out thesystem. The system shown in FIG. 4, therefore, is merely representativeof known systems for quickly and automatically reversing hydraulicdrives.

Means are also provided of a conventional nature whereby as the pistonrod 59 moves upwardly to a predetermined degree adequate toproperly lifthammer element 24 to a point of release, the valveconnections describedabove with respect to FIG. 4 will be quickly reversed so as to quicklyhydraulically drive the piston of actuator 49 downwardly and therebymove pulley.44 rapidly out of the way of the falling cable 34 wrappedtherearound. Thus, movement of a projecting finger or other protrusion61 carried by rod 59 ultimately serves to close a pair of contacts 62 soas to close the circuit of a power supply 63 and thereby energize asolenoid 64. As solenoid 64 is energized, it will act against the urgingof a spring 66 which otherwise serves to urge control element 58 to theposition shown in FIG. 4.

Thus, when solenoid 64 is energized, it can serve to quickly shiftcontrol element 58 in order to reverse the hydraulic connections toactuator 49.

Having the above arrangement in mind, it is readily apparent that cable34, as trained about pulley 44, forms first and second reaches 34a, 34bthereof. The first reach is directly coupled to move hammer element 24.Hoisting means, such as the winch 43, is coupled so as to anchor the endof the second reach 34b. The actuator 49 is provided with apredetermined stroke serving to move the pulley from a lower to an upperposition in order to elongate the second reach 34b while shortening thefirst reach by a multiple of the stroke of actuator 49. In this manner,if the stroke of actuator 49 is on the order of 2 feet, the hammerelement 24 will be raised a distance of 4 feet due to the interpositionof the rising pulley 44.

Additional multiplication of the actuator stroke can, of course, beobtained by introducing additional pulleys forming additional reaches ofcable 34.

Further, from the foregoing, it will be readily evident that pulley 44has less distance to travel when it is being returned, and accordingly,can move to its retracted position in less time and thereby more quicklyrelieve the strain on cable 34 to permit hammer element24 to fall andstrike its blow. It is apparent that pulley 44 only needs to beaccelerated downwardly from its upper position at a rate exceeding onehalf the acceleration rate provided by the force of gravity along. Thisfraction may be further proportionately reduced by introducingadditional pulleys to further subdivide the cable into additional reachportions.

In circumstances such as the above offshore support tower applicationwhere it is found necessary to drive piles below water level and wherethe piles are hollow, it has been observed that the column of waterentrapped within the pile can rise to a point where the anvil element 21acts directly against the column of water and thereby generates acompression wave, in the nature of a water hammer, capable of doingconsiderable damage due to the great forces developed by such wave.

In addition, a further problem exists of dissipating the energy of theblow which is struck by virtue of the column of entrapped liquid whichmust be forced from within the pile.

With reference to FIG. 5, another embodiment of the anvil element 21serves to solve the foregoing problems. Ac cordingly, an anvil element71 includes a striking face 72 at its upper end adapted to be struck bythe hammer element 73. The lower end of anvil element 71 includes ahollow recess 74 containing an inflated gas-filled bladder 76. Bladder76 may,

for example, be an inflated nylonneoprene hollow sphere" having anoutside diameter on the order of 1 foot or greater and a sufficientcapacity so that it can be inflated with air, for example, toaccommodate the hydrostatic head developedat the top of the submergedpile for the depth at which the pile is being driven. I

Thus, if anvil element 7 I is directly engaged on the upper end of thethickened wall portion 77 of pile 78 and the water level has risen to apoint where it may make direct contact with the exterior of bladder 76,the striking blow of hammer 73 will not transmit a shock wave throughthe liquid medium within pile 78 in view of the fact that thecompressive air within bladder 76 serves to initially absorb the shock.

The striking blow will, of course, serve to drive thcvpile 78 downwardlysomewhat and this can serve to develop additional compression by virtueof the upwardly displaced column of water contained herein. In order tovent this water column from within pile 78, flow passages 79 ofsubstantial diameter, for example, on the order of 4 or 5 inches, and ofa sufficient number are provided so as to quickly vent the liquid. Inthe event that the flow passages 79 are incapable of venting the liquidquickly enough to preclude the development of a shock wave in the liquidwithin pile 78, it will be readily apparent that bladder 76 will absorbthe momentary increase in pressure and thereby'provide additional timefor discharging the liquid without forming the compression wave.

Another embodiment for safe guarding against the development of acompression wave and for venting the water displaced by downwardmovement of the hollow pile is shown in FIG. 6.

Thus, a pile construction 81 has been provided comprised of an elongatedrigid hollow member 82 adapted to be driven in an upstanding orientationby a succession of blows applied at the upper end thereof. The upper endhas been prepared with a thickened wall portion 83. A closure plate 84serves to seal the upper end of pile 81 so as to entrap a cushion of airin the region 86 when lowering pile 81 into a body of water for driving.Openings 87 are formed at a predetermined displacement beneath closureplate 84 so as to vent the column of water 88 in response to compressionderived from the driving blows of the hammer element 89 as the pilemoves downwardly into the earth. The cushion of air in the region 86therefore serves to momentarily absorb the reactive forces of the columnof water 88 and to permit the flow passages formed by openings 87 tovent the column.

In another embodiment of the system for driving piles, as shown in FIGS.7 and 8, a support tower extension structure 91 supports the hoistingmeans and actuator structures described above at an elevation above thelevel of the top of the tower. An elongated cable 92 is suitably coupledto a bail 93 so as to lift and lower an improved hammer element 94,whereby a drop-hammer action can be obtained even while driving piles ata modest angle to the vertical.

Hammer element 94 is designed to strike blows upon the upper end 96 of apile 97 and includes a massive elongated guide stem portion 98 of a pile97 and includes a massive elongated guide stem portion 98 movable insliding relation coaxially within the pile 97 and further includes amassive head portion 99 formed on the upper end of stem portion 98. Theunderside of head portion 99 projects laterally to form a shoulder 101,which moves through a predetermined stroke S, to strike the upper end 96of pile 97 in driving the pile. A fluid passage 102 extendslongitudinally of guide stem 98 for relieving or venting fluid surgeduring the striking movement of hammer element 94.

Thus, as in the case of driving piles deeply into the ocean floor at aslight slant, batter piles can be driven by the drophammer system asdescribed above whereby the hammer is lifted and released from anoutdoor work station and the hammer can strike the upper end of the pileas contained in a leg 103 or other means defining a channel in which toguide and lodge the piles 97.

As thus provided, the embodiment described lastly above provides theadvantage of a drop hammer acting against the upper end of a pile beingdriven, while at the same time serving to permit the pile to be driveninto the earth at a substantial angle to the vertical.

While the systems disclosed herein overcome the problems involved inusing pile extensions and followers, it will be readily evident that thedisclosed systems are not incompatible with the sue of such extensionsand followers. Therefore, whenever they should necessarily be requiredin a given construction project, the disclosed systems can be employed.

It is also apparent that the systems disclosed herein open the door topractical use of much larger hammer elements having a mass an order ofmagnitude greater than conventional present day systems.

lclaim:

1. In a system for driving piles by a succession of blows struck fromabove by a hammer element, a driving head assembly adapted to transferthe blows to the upper end of the pile comprising an anvil elementadapted to engage the upper end of a pile in blow-transmitting relationthereto, an elongated hollow closed case secured at one end to the anvilelement to form an extension thereof, an outlet serving to vent liquidfrom within said case while generally retaining air pressure within thecase, means serving to supply air pressure to the interior of the case,a massive hammer element movable between advanced and retractedpositionswithin the case to strike said anvil at said advanced position, flexiblecable means connected to one end of said hammer element, and means foractuating said cable means to move said hammer element between saidpositions.

2. In a system for driving piles by a succession of blows applied to theupper end of a pile, a guide channel adapted to receive a pilelongitudinally inserted therein, a driving head assembly in the channelfor transferring hammer blows to the upper end of the pile, said headassembly including an anvil element in the channel disposed inblow-transferring relation with the pile to travel along said channeland follow penetration of the pile, and an elongated hollow closed casein the channel and secured at one end of the anvil element and movabletherewith in the channel, means for supplying air and movable with saidanvil to follow the pile during driving of the pile, and means formaintaining said case free of liquid during driving of the pile, meansforming a work station located on or above said body of water andsupported by said leg, actuator means carried by said work station andincluding a mechanical coupling to said hammer element extending fromsaid work station for moving said hammer element to strike said blows.

1. In a system for driving piles by a succession of blows struck fromabove by a hammer element, a driving head assembly adapted to transferthe blows to the upper end of the pile comprising an anvil elementadapted to engage the upper end of a pile in blowtransmitting relationthereto, an elongated hollow closed case secured at one end to the anvilelement to form an extension thereof, an outlet serving to vent liquidfrom within said case while generally retaining air pressure within thecase, means serving to supply air pressure to the interior of the case,a massive hammer element movable between advanced and retractedpositions within the case to strike said anvil at said advancedposition, flexible cable means connected to one end of said hammerelement, and means for actuating said cable means to move said hammerelement between said positionS.
 2. In a system for driving piles by asuccession of blows applied to the upper end of a pile, a guide channeladapted to receive a pile longitudinally inserted therein, a drivinghead assembly in the channel for transferring hammer blows to the upperend of the pile, said head assembly including an anvil element in thechannel disposed in blow-transferring relation with the pile to travelalong said channel and follow penetration of the pile, and an elongatedhollow closed case in the channel and secured at one end of the anvilelement and movable therewith in the channel, means for supplying air 3.In a system for anchoring a structure supported by hollow legstherebeneath, a hollow tubular leg of said structure disposed beneaththe surface of a body of water and engaging the floor beneath the bodyof water, a pile inserted longitudinally into said leg to be driven intothe floor beneath said body of water, an anvil in said leg fortransferring blows to said pile, a movable hammer element in said legfor striking blows upon said anvil, a closed case containing said hammerelement and movable with said anvil to follow the pile during driving ofthe pile, and means for maintaining said case free of liquid duringdriving of the pile, means forming a work station located on or abovesaid body of water and supported by said leg, actuator means carried bysaid work station and including a mechanical coupling to said hammerelement extending from said work station for moving said hammer elementto strike said blows.